The present invention relates to a microfluidic actuator, especially to an actuator that generates pumping force to a microfluid with a vacuum chamber.
Miniature pumps and valves have been a topic of great interest in the past 10 years. Many different pump and valve designs have been implemented by micromachining of silicon and glass substrates. Pumps and valves with pneumatic, thermal-pneumatic, piezoelectric, thermal-electric, shape memory alloy, and a variety of other actuation mechanisms have been realized with this technology. Although such pumps to date have shown excellent performance as discrete devices, often the processes for fabricating these pumps and valves are so unique that the devices cannot be integrated into a complex microfluidic system. Recently, paraffin actuated valves, and hydrogel actuated valves are being developed on the way to a more complex microfluidic platform.
Miniature analytical analysis systems, however, are demanding pumps and valves that are relatively small in size and can be integrated together on a single substrate. Systems to perform sample processing for DNA analysis are one such example. Such systems can require anywhere from 10-100 such pumps and valves to perform a variety of pumping, mixing, metering, and chemical reactions that are required to extract DNA from a sample, amplify the DNA, and analyze the DNA. To date no such technology exists to perform this type of microfluidic sample processing.
Anderson, et al. demonstrated the concept by using external air sources, external solenoid valves and a combination of thin film valves and vents on a plastic analysis cartridge. The entire sample handling for DNA extraction, in vitro transcription and hybridization was performed in a prototype system. See: xe2x80x9cMicrofluidic Biochemical Analysis Systemxe2x80x9d, Proceedings of Transducers ""97, the 9th International Conference on Solid-State Sensors and Actuators, Chicago, Jun. 16-19, 1997, 477-480 and xe2x80x9cA Miniature Integrated Device for Automated Multistep Genetic Assaysxe2x80x9d, Nucleic Acids Research, 2000 Vol 28 N 12, e60.
Recently, Mathies et al. employed the same technology to perform a polymerase chain reaction (PCR) followed by a capillary electrophoresis (CE) analysis on the same device (xe2x80x9cMicrofabrication Technology for Chemical and Biochemical Microprocessorsxe2x80x9d, A. van den Berg (ed.), Micro Total Analysis Systems 2000, 217-220). For applications in which sample contamination is of concern, such as diagnostics, disposable devices are very appropriate. In this case the manufacturing cost of such a device must be extremely low.
i-STAT corporation currently markets a disposable device that analyzes blood gases as well as a variety of ions. The i-STAT cartridge uses external physical pressure to break on-chip fluid pouches and pump samples over ion-selective sensors (i-STAT Corporation Product Literature, June 1998). In a similar manner, Kodak has developed a PCR-based HIV test in a disposable, plastic blister pouch (Findlay, J. B. et al., Clinical Chemistry, 39, 1927-1933 (1993)). After the PCR reaction an external roller pushes the PCR product followed by binding, washing and labeling reagents into a detection area where the PCR amplified product can be detected. The complexity of such systems as these is limited in part by the means of pressure generation. The simplicity of these approaches however is quite elegant.
Disposable, one-shot microfabricated valves have been implemented by a few researchers for diagnostic applications. Guerin et al. developed a miniature one-shot (irreversible) valve that is actuated by melting an adhesive layer simultaneously with the application of applied pressure of the fluidic medium. See: xe2x80x9cA Miniature One-Shot Valvexe2x80x9d, Proceedings of IEEE conference on Micro-Electro-Mechanical Systems, MEMS ""98, 425-428. In this invention, if the applied pressure is high enough the melted adhesive layer gives way and the fluid passes through the valve.
Another one-shot type valve has been developed by Madou et al. in their U.S. Pat. No. 5,368,704, xe2x80x9cMicro-electrochemical Valves and Methodxe2x80x9d. Here the valve is actuated by the electrochemical corrosion of a metal diaphragm.
While complex microfluidic systems have been demonstrated using external air supplies and solenoid valves, a need exists for complex microfluidic systems in more portable instrument platforms. It is thus necessary to provide an actuator that provides actuation sources and that can be equipped directly on the device in which the actuator is used.
The objective of the present invention is to provide a one-time microfluidic actuator.
Another objective of this invention is to provide a microfluidic actuator that is easy to prepare under a relatively low cost.
Another objective of this invention is to provide a microfluidic actuator with a vacuum chamber.
Another objective of this invention is to provide a microfluidic module comprising an actuator with a vacuum chamber.
Another objective of this invention is to provide a microfluidic device wherein the actuation sources are directly prepared on the device itself.
Another objective of this invention is to provide a novel method for the preparation of a microfluid module comprising a vacuum chamber actuator to actuate the microfluidic functions.
According to the present invention, a simple microfluidic actuator is disclosed. The microfluidic actuator of this invention comprises a sealed vacuum chamber. The vacuum chamber is actuated by providing a current to a thin film heater, which in turn weakens and, under the atmospheric pressure differential, punctures a diaphragm sealing said vacuum chamber whereby the vacuum inside said chamber is released. By applying the microfluidic actuator of this invention to a microfluidic network, the resulting pressure differential can be used to generate a pumping force within the microfluidic network. In the preferred embodiments of this invention, the chamber may be prepared in a silicon, glass, or plastic substrate and a diaphragm is vacuum bonded to seal the chamber. The diaphragm may comprise a metallic gas-impermeable film. A releasing member comprising a thin-film metallic heater is then microfabricated on the diaphragm. The assembly so prepared may be bonded to a glass or plastic substrate that contains a network of microchannels. The invented microfluidic actuator is suited for a microfluidic platform in generating driving forces for operations including pumping, metering, mixing and valving of microfluidic samples.
These and other objectives and advantages of the present invention may be clearly understood from the detailed description by referring to the following drawings.